Process for improving injectivity in secondary oil recovery



Patented Jan. 9, 1362 T fie 3,016,352 PROCES FOR TMPROVHNG HUECTHVTTY TN SECONDARY OIL REQOVERY Frederick A. irlessel, Montclair, Ni, assignor to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 30, 1959, Ser, No. 849,7d9

4 (Ilaims. (Cl. 252-855) This invention relates to the secondary recovery of petroleum by the water flooding method and more particularly is concerned with the treatment of water input wells for the purpose of facilitating the injection of flood water into an oil reservoir.

Oil exists in well sands or similar strata in two difierent states, i.e., as free oil that is' located in the voids of the sand and as fixed oil which is held by absorption (and perhaps to some degree by adsorption) on the particles of sand and which is commonly referred to as the film of oil that adheres to the particles of sand or the particles of the oleiferous structure. Such fixed Oil may be said to be held by sorption.

Free oil can be recovered by. conventional methods of oil producing such as draining the oil in conjunction with liquid or gaseous pressure and creating an artificial fluid or gaseous pressure in-the sand bed so as to dislodge the oil from the sand bed and thereafter conduct the dislodged oil to'the surface of the ground. Fixed oil, on the other hand, cannot be recovered by any of the conventional methods or means used to produce oil and cannot be dislodged economically by either fluid or gaseous pressure. In some cases, the amount of oil remaining in the well after pumping has become unprofitable may equal 60 percent of the original oil present. Water is introduced under pressure into a number of wells, and oil together with water is produced from other wells by the resultant water drive. The success of the water flooding operation manifestly depends upon its totalcost being less than the value of the additional oil recovered from the reservoir.

A substantial factor in the economics of water flooding is the cost of pumping the water into the formation. In many cases pumping costs may be too high to permit this secondary method to be employed successfully. This is occasioned by unduly low rates of Water injectivity into 7 the formation for a given pump pressure, which necessitates the use of excessively high pressures to force the water into the formation at the desired rate. When this condition prevails, a conventional flooding operation cannot be practiced economically.

The present invention is directed to a method of treating an input well so that the Water injectivity rate can be substantially increased for a given pump pressure level.

According to the invention, the formation adjacent the input well is treated by means of a water miscible organic treating agent which has the ability to increase the injectivity rate of water or brine solutions in an oil bearing formation. The organic treating agents, used according to this invention, are compounds having the following general formula:

Hie-eons wherein X represents either oxygen, an imino group (NH) including lower alkyl (1 to 4 carbon atom) substituted (NR) imino groups wherein R represents an alkyl group of l to 4 carbon atoms. The compounds are completely miscible with water, and when used to treat formation surrounding the input well base, a Substantial increase in the water or brine injectivity rate is eliected.

Examples of specific compounds contemplated by the foregoing general formula and which may be used in practicing the present invention include: 'y-butyrolactone, Z-pyrrolidone, and l-methyl, 2-pyrr0lid0ne, l-ethyl, 2-pyrrolidone, l-isopropyl, 2-pyrrolidone and l-butyl, 2-pyrrolidone.

The ability of these compounds to increase the injectivity rate of water or brine into an oil bearing formation was demonstrated in the following manner:

Eight core samples each measuring 3 inches in diameter and 4 inches in length of an oil bearing formation were obtained at a depth of approximately 1300 feet from the Bartlesville sand, Washington county, Oklahoma. These core samples had the following properties:

Permeabih Percent Saturation Sample Number ity. Md. Porosity (Milli- (Percent) darcies) Oil Water Total Core No.:

A simple mounting provided means for flooding the sur-. face of the cores. The samples were treated as follows:

Core No. 1 Treated with 10 cc. of water. Core No. 2 Treated with 10 cc. of Arbuckle lime brine (obtained K 8: S Project Oil Recovery Corp., Miller WSW#1 well, Township 27 north, Range 13 east, NW. quarter of Section 5, Washing ton County, Oklahoma).

First treated with 2 cc. Followed within 15 minutes by Core No. 3. -butyrolactone (B.P. 240 C.) 10 cc. Water. Core No. 1 'y-butyrolactone 10 cc. Arbuckle Lime brine. Core N0. 5 2-pyrrol1done (B.P. 245 C.) 10 cc. water. Gore No. 6 2-pyrro1idone 10 cc. Arhuckle Lime brine. Core No. 7 l-methyl, 2-pyrrolidone 10 co. water. Core No. 8..-. l-methyl, Z-pyrrolidone 10 ee. Arbuckle Lime brine.

The number of minutes for the absorption of water or pounds which are soluble in water have nevertheless the ability to increase materially the injectivity of water and brine in an oil bearing formation. It is well known that an increase in water throughput in a given formation helps materially in the recovery of oil. a

The following example further illustrates the use of the present invention.

A water input well in an oil bearing formation being subjected to a water flooding operation located at a depth of about 1300 feet and having an oil sand thickness of 22 feet was selected. Core studies showed that the formation had an average porosity of 17%, a permeability to air of about 40 millidarcies and a residual oil content of 35%. Prior to treatment the rate of pumping water into this input well was about 200 barrels per day. The formation was then treated by pumping thereinto, through the Water input well, 20 gallons of l-methyl, Z-pyrrolidone. The pumping of fiood water into the input well was then resumed with the same pump pressure with the result that the injection rate was more than double that obtained prior to treatment.

It is not known why treatment with the type of compounds described above will substantially increase the permeability of an oil bearing formation to water or the injectivity rate of water or brine into the input wells. One possible explanation is that these compounds in some manner help to move the droplets of residual oil that otherwise would not flow through the formation. By fioW- ing this residual oil away from that portion of the formation adjacent to the pore hole of the input well, the resistance to water flow is considerably reduced and the injection of water is correspondingly facilitated, possibly due to the fact that a greater area of oil free sand is now present for the injection of the water. Once the removal of residual oil from the immediate vicinity of the pore hole has been accomplished, the resistance to flow of water will remain low during further injection of water or brine. It is understood, however, that we do not limit ourselves to this theory of operation.

I claim:

1. In the secondary recovery of petroleum from an underground formation by the water flooding method wherein X represents a member of the group consisting of 0 and an imino group and a lower alltyl (l to 4 carbon atom) substituted imino group.

2. The method according to claim 1 wherein the compound introduced through the well is -butyrolactone.

3. The method according to claim 1 wherein the compound introduced through the Well is 2-pyrrolidone.

4. The method according to claim 1 wherein the cornpound introduced through the well is l-methyl, 2-pyrrolidone.

References Cited in the file of this patent UNITED STATES PATENTS Lietz Nov. 11, 1941 OTHER REFERENCES Oreo Pins Hopes on Carbonated Flood Water, Article in the Oil and Gas Journal, Sept. 2, 1957, pages 88 and 89. 

1. IN THE SECONDARY RECOVERY OF PETROLEUM FROM AN UNDERGROUND FORMATION BY THE WATER FLOODING METHOD WHEREIN WATER IS INJECTED THROUGH AN INPUT WELL INTO AN UNDERGROUND OIL BEARING FORMTION TO FORCE THE OIL THROUGH THE FORMATION TOWARD AN OUTPUT WELL FROM WHICH OIL IS WITHDRAWN, THE STEP OF INCREASING THE INJECTIVITY OF FLOOD WATER INTO AN INPUT WELL WHICH COMPRISES INTRODUCING THROUGH THE INPUT WELL INTO THE ADJACENT FORMATION A WATER MISCIBLE COMPOUND OF THE FORMULA 